1. Field of the Invention
The present invention relates to a screw post, and more specifically, to a screw post utilizing cooperating of an approximately triangular hollow structure formed therein with reinforcement ribs for preventing itself from cracking.
2. Description of the Prior Art
In general, a self-tapping screw utilizes its positive threads to generate corresponding negative threads on an inner wall of a screw hole so as to be screwed into the screw hole tightly. Chips cut by the positive threads of the self-tapping screw may clog up between the positive threads and the negative threads so as to apply a radial pushing force upon the screw post. Thus, the screw post could receive a considerable circumferential stress. When the aforesaid circumferential stress is excessive, the screw post may crack accordingly.
For solving the aforesaid problem, a crack preventing design could be applied to the self-tapping screw. For example, in the prior art, one cutting opening (or more) is formed at the bottom end of the self-tapping screw. As a result, chips cut by the positive threads of the self-tapping screw may fall onto the bottom of the screw hole via the cutting opening instead of clogging up between the positive threads of the self-tapping screw and the negative threads of the screw hole, so as to reduce the aforesaid circumferential stress. In another example, the sectional contour of the self-tapping screw could be an approximate triangle. As a result, the space between the sides of the approximately triangular section of the self-tapping screw and the inner wall of the screw hole could be utilized to contain more chips cut by the positive threads of the self-tapping screw, so that the aforesaid circumferential stress could also be reduced. However, all the aforesaid designs may increase the manufacturing cost of the screw post.
The prior art could also utilize a design in which reinforcement ribs are additionally disposed on the outer surface of the screw post. For example, please refer to FIG. 1, which is a diagram of a screw post 10 according to the prior art. As shown in FIG. 1, the screw post 10 includes a post body 12 and four reinforcement ribs 14. The post body 12 has a cylindrical hollow structure 16. The four reinforcement ribs 14 protrude from an outer surface 18 of the post body 12 in an axial-extending manner and are arranged radially. In such a manner, via disposal of the four reinforcement ribs 14, the maximum circumferential stress that the screw post 10 could withstand is accordingly increased. However, this design may also increase the manufacturing cost of the screw post 10. Furthermore, this design could only provide the screw post 10 with a partial reinforcement effect. Thus, this design could not efficiently prevent cracking of the screw post 10 since the aforesaid circumferential stress is distributed uniformly along the outer surface 18 of the screw post 10.
Furthermore, since the screw post is usually formed by an injection forming process in the prior art, a weld line would be accordingly formed at a position of the screw post where its structural strength is lower. Therefore, the screw post may crack easily at the position corresponding to the aforesaid weld line.